Not Applicable.
Not Applicable.
1. Field of Invention
The present invention relates to a composition of a lanthanum (a rare earth element) concentrate, a process for manufacturing of the composition, and a process for using the composition to remove the toxic forms of selenium and arsenic from water. In particular, the composition uses lanthanum oxides in conjunction with other oxides to form a filtration media that does not dissolve to any great extent in water that it is filtering.
2. Description of the Related Art
The need for potable water is currently being recognized as a high priority for governments worldwide in response to growing populations in areas with limited water supplies. This is particularly true for the United States with projections of continued population growth over the next several decades in its Southwest and Northeast regions. It is these western regions, which have large areas of desert, which by their definition have limited rainfall and corresponding limited water resources. As a result, municipalities of growing population centers in these areas are increasingly tapping into and relying upon large underground aquifers (well water supply) to obtaining the necessary water supply for their growing communities. On the eastern portion of the United States, where there is limited reservoir water supplies, municipalities face the same challenge as new population growth in that area has also pushed the demand for increased aquifer fed water supply.
Although there are concerns regarding the pollution of underground water from mining, refining, manufacturing and other industrial type operations and concerns, toxins, including elements such as arsenic, selenium and other elements are also naturally found in the ground where water aquifers are present and naturally xe2x80x98contaminatexe2x80x99 the water percolating through such aquifers. When such toxic elements leach from natural underground deposits into well saturated aquifers, the toxic elements will, over a period of time, spread throughout and dilute into very small minute trace non-hazardous amounts. However, under drought conditions when such aquifers are not fully replenished by natural rain or snow fall, such toxic water-borne elements concentrate into unacceptably dangerous concentrations which are injurious to human heath when ingested.
In other areas, such as India and China, the two most populous countries in the world, naturally occurring underground deposits of arsenic and selenium contaminate the drinking water. In some areas of these countries, the situation is so dire that arsenic and selenium water poisoning has become unavoidable and causes chronic or fatally acute poisoning.
There is also concern by many industrialists, who take great pride in maintaining green and environmentally friendly operations, to properly ensure that any industrial effluent be cleansed of any toxins before being released into the open environment. To meet this challenge, industrialists often meet, then exceed, current and future governmental environmental mandates regulating the waste discharge from industrial concerns. At the same time, in order to remain competitive, industrialists try to find pollution control means that are economic and practical in reclaiming harmful elements from waste discharge that might have any contact with outside bodies of water, both above and below ground.
Of the two contaminates in concern, the element Arsenic (As) is a metal commonly found in nature and can naturally contaminate underground water supplies. It is naturally found in an ionic form (the xe2x88x923, 0, +3, and +5 oxidation states). This means that when the element has excess or a depletion of its negatively charged electrons (exe2x88x92), the element becomes a charged ion (e.g., Asxe2x88x923). When arsenic (As) gains three electrons (3exe2x88x92) in addition to its normal complement of electrons (exe2x88x92), arsenic (As) converts to its xe2x88x923 oxidation state to become the negatively charged ion form of the element, Asxe2x88x923. When arsenic (As) loses five electrons (5exe2x88x92) from its normal complement of electrons (exe2x88x92), this gives arsenic (As) its positive oxidation state or the positive ionic form of As+5. Arsenic (As) loses its electrons (exe2x88x92) when it is dissolved into water (H2O). At that time, the oxygen (O) from water cleaves off from the hydrogen (H2) to form new ionic compounds with the ionic forms of dissolved arsenic. The most common forms of ionic arsenic found in drinking water and wastewater streams being (As+3) and (As+5). These arsenic ions combine with negatively charged oxygen ions (Oxe2x88x92) called oxygen anions or oxyanions.
The toxicity of arsenic (As) dissolved in water depends on the arsenic""s oxidation in water. Arsenate (As+5) is reported to be less toxic that arsenite (As+3) and other forms of arsenic based compounds such as methylated arsenic and the like. The level of arsenic (As) in water beyond 0.05 micrograms per liter (ug/l) is known to cause carcinogenic effect in human beings. The United States Environmental Protection Agency (EPA), in monitoring the health and environmental concerns regarding arsenic (As) levels in water, has promulgated a new Maximum Contaminant Level (MCL) of 10 parts-per-billion (ppb) in drinking water (i.e., ten parts of arsenic per billion parts of water). Under federal mandates, any water having higher levels of arsenic (As) than the MCL will be found to be unfit and dangerous for human consumption.
Selenium (Se), the other element of toxic concern, is also a naturally occurring element. In comparison with Arsenic (As), however, selenium (Se) is naturally found in much smaller quantities so as to be considered an essential trace element, which is practically nontoxic. Like arsenic (As), selenium (Se) can be found in an ionic form in water such as selenite, Se+4 and selenate, Se+6 where it loses its electrons (exe2x88x92) when it dissolves into water (H2O). The oxygen (O) cleaves off from the hydrogen (H) of the water to form a new ionic compound with the selenium (Se). The oxygenated ionic forms of selenium (Se) are selenite (Se2Oxe2x88x922) and selenate (Se3Oxe2x88x922), respectively.
In nature, the deficiency of selenium (Se) in some animal diets, such as the longhorn sheep, can cause weakness in the animals""young. On the other extreme, the over accumulation of selenium (Se) in the locoweed, as consumed by cattle, horses and the like, can cause the imbibing animal to exhibit manic characteristics.
It is, however, the presence of various man-made compound forms of selenium (Se) in water that is of the most environmental concern. Selenium (Se) compounds such as hydrogen selenium, selenium sulfide, selenium dioxide (SeO2), selenium oxychloride (SeOCl2) and the like are extremely toxic and can resemble arsenic (As) poisoning in their physiological reactions.
In order to address these environmental concerns of the presence of Arsenic (As) and Selenium (Se) compounds in aqueous (water) solution, either as naturally occurring in water or as part of the reclamation of such chemicals from industrial waste water or runoff, various techniques have been developed so that water, whatever its source, can be purified of these harmful chemicals to make the water safe for drinking.
The removal of Arsenic (As) from water can be accomplished through chemical precipitation of arsenic (As) though the addition of lime, alum or an iron salt at an appropriate acidity (pH) to the contaminated water. The combination of the Arsenic (As) with lime or salt will cause the arsenic (As) to form a insoluble compound that solidifies or precipitates out of the water for easy removal. Other scientific methods rely on the removal of the ionic form of the element from contaminated water using techniques such as ion exchange, reverse osmosis, electrolysis or distillation. These techniques rely on the ionic form of the toxic element/compound being smaller or lighter than water, or the electrical charge of the ion distinguishing the ion and separating it out from water. These techniques, which are generally recognized for removing toxic heavy metals from water, are less effective with selenium (Se) or arsenic (As) and are especially limited both economically and for purifying great volumes of water. It can be very difficult for these conventional heavy metal removal methodologies to remove trace amounts of arsenic (As).
Still other water treatment methods have been employed to achieve acceptable removal of arsenic from contaminated water, including the use of immobilized iron (Fe+3) in the form of micro particulate iron oxides, iron loaded cation exchange resins; and activated alumina (aluminum oxide or Al2O3). All of these methods are expensive and require labor-intensive process management. Most methods fail to provide a reduction in contaminants sufficient to meet the new EPA/NSF standards for drinking water.
Aqueous decontamination of Selenium (Se) can be accomplished when the dissolved form selenium (Se) is in its water based ionic forms of selenite (Se2Oxe2x88x922) (i.e., Se+4) and selenate (Se3Oxe2x88x922) (i.e. Se+6). In this form, precipitation methodologies treat the selenium (Se) contaminated water with an iron (Fe) salt such as ferric or ferrous oxide, chloride, or hydroxide or with Aluminum (Al) or Zinc (Zn) in some appropriate form such as powder or granules which causes the precipitation of the resulting insoluble compound containing the selenium (Se). However, the above methodology only has limited effect on the ionic form of selenium Se+6. As a result, other extraction methodologies such as ion exchange or reverse osmosis are used, although as discussed earlier, these treatments are not economical for treating large quantities of contaminated water.
One other purification technique for water contaminated with ionic forms of selenium or arsenic is using oxide forms of the elements lanthanum (La) and aluminum (Al) which are lanthanum oxide (La2O3) and alumina (aluminum oxide, Al3O2), respectively. The U.S. Pat. No. 5,603,838 issued Feb. 18, 1997 to Misra, et al (hereinafter ""838 patent) teaches that lanthanum oxide (La2O3) by itself or together with alumina (i.e., aluminum oxide or Al3O2) can remove ionized forms of arsenic (As) and selenium (Se) in contaminated water.
Both elements, lanthanum (La) and aluminum, are normally found naturally in ores and are normally found bound with oxygen (O2) to make oxides or ceramics. The ""838 patent teaches the use of lanthanum oxide (La2O3) by itself or combined with alumina (aluminum oxide, Al3O2) where the resulting composition contains ten (10%) percent to one hundred (100%) percent of lanthanum oxide (La2O3). The gamma activated or commercial grade alumina (aluminum oxide, Al3O2) is used in substitution since the alumina is much less expensive than the pure lanthanum oxide (La2O3) and decreases the overall cost of the resulting composition.
According to the ""838 patent, the granules of lanthanum oxide (La2O3) or granules of lanthanum oxide (La2O3)-alumina (aluminum oxide, Al3O2) composition are placed in a packing column. The packing column consists of a glass cylinder with an open top that receives the contaminated water and a narrow opening at the bottom which regulates the flow of water going through the column and hence the contact time of the contaminated water and the lanthanum granules in the column. The selenium (Se) and Arsenic (As) contaminated water is introduced at the top of the column and passed through the column, where it is collected from the bottom end of the column and reintroduced at the top for recirculation from five (5) to thirty (30) minutes.
The actual testing of the samples in ""838 patent was accomplished by placing the lanthanum oxide (La2O3) or a compound of lanthanum oxide (La2O3)-alumina (aluminum oxide, Al3O2) in a flask containing selenium (Se) and arsenic (As) contaminated water. The flasks were then swirled to mix the oxides and the contaminated water. The mixture was then poured through Whatman number 5 filter paper and the filtered water was then tested for presence of selenium (Se) and arsenic (As) presence.
The sample testing showed that lanthanum oxide (La2O3) or lanthanum oxide (La2O3)-alumina (aluminum oxide, Al3O2) composition did successfully and significantly remove the presence of selenium (Se) and arsenic (As) from the contaminated water. In simple terms the oxide or oxide composition in granular form acted as xe2x80x9cflypaperxe2x80x9d to remove the selenium (Se) and arsenic (As) ions from the contaminated water.
To release the selenium (Se) or arsenic (As) from the lanthanum oxide (La2O3) or lanthanum oxide (La2O3)-Alumina (aluminum oxide, Al3O2) compositions, the oxide/oxide composition was washed with a solution of sodium hydroxide (NaOH) to remove the absorbed selenium (Se) and arsenic (As) ions.
The ""838 patent disclosed that lanthanum (La) is effective as a removal agent for selenium (Se) and arsenic (As) because the high positive charge of the grain surface of the lanthanum oxide (La2O3) attracts the highly negative charged oxyanions of selenium (Se) and arsenic (As) in order to make lanthanum oxide (La2O3) a very effective water contaminate removal agent.
However, there are two remaining issues from ""838 patent methodology that seriously impede, or make impossible, the grand scale application of this technique to treat vast amounts of selenium (Se) and arsenic (As) contaminated water. First, the expense of refined lanthanum oxide (La2O3) as used in this operation is cost prohibitive.
Secondly, the lanthanum oxide (La2O3) does not bind well to itself or to alumina (aluminum oxide, Al3O2). Lanthanum oxide (La2O3) dissolves when contacted with water and washes away in the water along with those pollutants adhering to it.
Likewise, attempts to use lanthanum based oxides and compounds as taught in U.S. Pat. No. 5,053,139 issued to Dodwell in 1991 (hereinafter ""139 patent), such as complex lanthanides fused alumina, iron, silica and other xe2x80x9ccarrierxe2x80x9d media in order to provide a product of suitable particle size and affordability to be useful as a filtration media, also have seen the above described limitation on their effectiveness. Complex lanthanides such as lanthanum silicate, as used in silica gel-based filtration devices, have the same tendency of standard lanthanum oxide, to xe2x80x9cwash awayxe2x80x9d from the carrier grains to which they were originally bound.
This washing away of lanthanum oxides/complexes includes reduction in the size of a lanthanum oxide/complex granular media down to a very fine particulate state, which eventually causes the blockage of any downstream filters or filtration devices. Worse, the escape of the lanthanum media and its bound contaminants from the filtration containment vessels results in the unwanted (and unsuspected) release of potentially toxic concentrations back into a supposedly purified water supply.
There have also been other attempts, in the field of ceramics, to fuse lanthanum oxide to the outside surface of alumina grains at high temperatures in order to reduce the high expense of technical or even more expensive research grades of lanthanum oxides for use in the lanthanum oxide/composition filtration. Even though fused, lanthanum oxide still has a weak bonding capability and will wash away from the alumina grain in the presence of water.
What is needed therefore, is a practical, cost-effective, lanthanum-based composition and process, which will prevent or significantly reduce the dissociation or washing away of the lanthanum oxide in the presence of water. This will allow large-scale application of lanthanum oxide purification for vast bodies of water and further reduce the likelihood of downstream blockage of standard filtration systems from the resultant undesired release of lanthanum oxides/pollutant complexes downstream from a filtration process.
The present invention consists of a composition and process lanthanum oxide media that is suitable for composing an inexpensive filtration media that effectively removes arsenic and selenium contaminates from water. Lanthanum oxide media also will not allow the lanthanum oxide to wash away or disassociate itself from the carrier grain in the presence of water; thereby preventing causing downstream blockage of a filtration system or allowing release of filtration media downstream of the filtration system for contamination of supposedly purified water. Further, the invention will allow the lanthanum oxide based filtration media to be used satisfactorily in large-scale water purification systems (e.g., municipal water treatment facilities) that handle tremendous quantities of water.
The invention is a composition comprising of lanthanum oxide and at least one oxide from a group consisting of neodymium oxide (Nd2O3), cerium oxide (CeO2), praseodymium oxide (Pr6O11), strontium oxide (SrO), calcium oxide (CaO) and sodium oxide (NaO).
The process of making the composition consists of using as a base, a lanthanum concentrate available from Molycorp, Inc. Mountain Pass Calif. as product entitled Code 5210 Lanthanum Concentrate. The concentrate comes as a granular media granular size range of 0.84 mm-0.25 mm which is suitable for use with a standard water filter using a 60-20 mesh. The granular media is then sintered to fuse the oxides in each grain together. The sintered media is then washed to remove any loose or unsintered particulate matter away from sintered media.
In use, the first step has the sintered lanthanum oxide concentrate media placed in contact with aqueous solution containing arsenic and or selenium in their oxyanion form (i.e., (selenite, selenate, arsenate and arsenite). The oxyanion in the solution binds with the sintered lanthanum oxide concentrate to form an insoluble complex comprising of lanthanum oxide and said oxyanion. The solution is then removed from said insoluble complex.
It is an object of this invention to provide a practical, economical, easily manufactured, filtration media that can effectively remove arsenic and selenium from an aqueous solution. It is another object of this invention to provide a filtration media that removes arsenic and selenium from an aqueous solution without significantly dissolving in water. It is a further object of this invention to provide a lanthanum oxide filtration media that will not break down into fine particulate matter thereby blocking downstream filtration devices. It is yet another object of this invention to provide a lanthanum oxide filtration media that will prevent the downstream release of aqueous contaminates.